///2009 Abstract Details
2009 Abstract Details2019-08-03T15:55:31-06:00

Up-down determination of the ED90 of the initial rate of of infusion of phenylephrine for the prophylaxis of spinal induced hypotension in parturients undergoing cesarean delivery

Abstract Number: 196
Abstract Type: Original Research

Namtip Triyasunant MD1 ; Ronald B George MD FRCPC2; Dolores M McKeen MD MSc FRCPC3; Ashraf S Habib MB ChB MSc FRCA4

Introduction: Hypotension occurs commonly following spinal anesthesia for cesarean delivery (CD) with a reported incidence of up to 80% (1). This study is designed to determine the ED90 for an infusion of phenylephrine to prevent spinal induced hypotension in parturients presenting for an elective CD.

Methods: With REB approval, non-laboring, age ≥ 18, term gestation, ASA I-II parturients presenting for CD with spinal anesthesia were enrolled. Parturients with BMI ≥ 45kg/m2, height<150 cm, hypertensive disease of pregnancy, severe maternal cardiac disease, and fetal anomalies were excluded. We measured blood pressure three times (Q2minutes), prior to going to the operating room with the subject supine with left uterine displacement. The anesthetic technique was standardized. Spinal anesthesia was administered at L3-L5 in the sitting position with 12mg bupivacaine, 15mcg fentanyl, and 150mcg morphine. Each subject received an intravenous coload of crystalloid (~ 15 - 20 ml/kg). Blood pressure was measured every 1 minute for the duration of the study (after placing the spinal anesthetic until the birth of subjects child). The infusions were prepared in 60 ml syringes and the dosage was varied such that all infusion were infused at 30 ml/hour. The anesthesia provider was blinded to the dose of phenylephrine, as was the subject. The study infusion was started immediately following the injection of intrathecal medications. We started with an initial dose of phenylephrine 50 mcg/min. The subsequent dose is based upon the response of the preceding subject in a biased-coin design up-and-down method (2). Success (i.e. a positive response) is defined as the subject experiencing no hypotension (mean SBP - 20% or < 90 mmHg). Failure is defined as the subject experiencing > 1 episode of hypotension. If a positive response is observed, the next subject is randomly assigned with probability of 0.10 to the next lower dose and with probability 0.90 to the same dose. If a failure is observed in the previous subject, the dose is stepped up in the next subject. The dosing changes are in increments of 10 mcg/min. Hypertension (mean SBP + 20%) or bradycardia (HR< 50/min) was treated by reducing the infusion by 50% (15 ml/hour). Any further hypertension or bradycardia resulted in stopping the infusion.

Result: Twenty-seven of forty subjects have been successfully recruited. The mean age and BMI is 30.7 5.0 years and 32.8 4.6 kg/m2 respectively. The median parity is 1 and gestational age is 39. Three subjects have experienced hypotension and required additional vasopressors. No subjects have experience hypertension, bradycardia, or any other adverse events. No unblinding or interim analyses were done. Recruitment is expected to be complete by March 2009. Complete results will be available before the 2009 SOAP meeting in Washington.

References: 1. Br J Anaesth 2006;96:95-9. 2. Anesthesiology 2007;107:144-52.

SOAP 2009